Regression analyses of In([n-butane]/[ethane]) and ln([propane]/[ethane]) relationships for all observations (a) and two transport patterns (b), (NATL and NA-anthro). The dotted lines in both figures indicate the mixing-only trend initiated from an assumed origin (upper right end) based on concentrations in emissions. The solid lines with scales show the photochemical decay slope from the same origin for a fixed OH concentration defined in the text. In both figures,the black dots show the data for all available paired measurements (including data that do not belong to any defined transport patterns). The method to compute the slopes is discussed in the text. The legend provides, for all observations and the two transport patterns, linear regression slopes, correlation coefficients, and p values. DOI: https://doi.org/10.1525/elementa.194.f7